Copper fin tube Raypak heater noise

DF

I am working on a multi-family residential building where they have two Raypak copper fin tube domestic hot water heaters on the roof. Good heaters. 30 years old and still work well. However, they make a loud clicking noise every time the heaters kick on and off. Resident in unit below can clearly hear it in their bedroom. One rep from Raypak says that the burner needs to be replaced. Another says that the noise will not go away due to the age of the equipment??? Any thoughts?

hot_rod

A single click like a relay engaging?

When that type of boiler gets a lime scale deposit building up inside you can get a percolation sound. Think of an old tea kettle with a layer of deposits on the bottom.

When the burner kicks on you may hear this as the burner is heating through the mineral layer.

When it shuts off it May be noise from the hot copper cooling and contracting.

Really need to be in front of it to better diagnose the noise.